This invention relates to a magnetic circuit and in particular to a use of silicone rubber for relieving material stress in magnetic material in a magnetic circuit.
When two pieces of magnetic material are clamped together in a magnetic circuit, it is often necessary to control the clamping pressure so as not to stress the material along the clamping surfaces. This is particularly true where, as in the case of YIG-tuned filters, all parameters of the magnetic circuit are critical. Such resonators are disclosed, for example, in U.S. Pat. No. 3,544,918 issued Dec. 1, 1972 to W. E. Venator, Jr., and U.S. Pat. No. 3,879,677 issued Apr. 22, 1975 to C. A. Arnold. One of the conventional methods of reducing the effects of material stress under such circumstances was to make the clamp surface area much larger than the pole tip surface area. If the clamping surface area is made sufficiently large, the flux density thereacross may correspondingly become so low that the effects of material stress are insignificant. Making the clamping surfaces large adds weight to the magnetic circuit, however, and it is not desirable or even practicable in many applications to use large clamping surfaces. In such cases, spring clamping or controlling screw torque has been used, but neither of these previous methods is very satisfactory because they do not stand up well under shock or vibration.
As for the effects of temperature change on the material stress, none of these prior art methods mentioned above provides any compensation for thermal expansion, or eliminates stress hysteresis to be described later.